1. Field of the Invention
The present invention relates to a liquid applying apparatus and an ink jet printing apparatus, and specifically, to a liquid applying apparatus that applies a liquid to a medium for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials. Likewise, the present invention relates to an ink jet printing apparatus comprising a mechanism that applies the liquid to a print medium used for ink jet printing, for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials.
2. Description of the Related Art
A spin coater, a roll coater, a bar coater, and a die coater are known as systems for applying a liquid or an aqueous material to various media. These applying systems are premised on continuous applying on relatively long applying media. Thus, for example, if liquid is applied to applying media having a relatively small size and being intermittently conveyed, paint beads may be disturbed at a position at which the applying is started or ended. In this case, the coats obtained may be nonuniform among the applying media.
A known configuration that can solve this problem is described in Japanese Patent Application Laid-open No. 2001-070858. On the basis of the die coater system, this configuration uses a rotating rod bar and ejects a paint to the rod bar through an ejection slit to form a coat on the rod bar. The coat formed is contacted with and transferred to an applying medium as the rod bar rotates. In this case, when the coat formed on the rod bar is not transferred or applied to the applying medium, the paint is returned to a head by the rotation of the rod bar. The paint is then collected via a collecting slit. In other words, the rod bar continues to rotate even during non-applying, while the paint is being formed into a coat on the rod bar. This enables a uniform coat to be obtained even if the applying media are intermittently supplied and applied with the paint.
Even in the field of ink jet printing apparatuses, those using a liquid applying mechanism are known. Japanese Patent Application Laid-open No. 2002-517341 describes an apparatus which uses a doctor blade contacting with a roller and in which the application liquid is collected between the blade and the roller so that the application liquid is applied to the roller as the roller rotates. As the roller rotates, the application liquid applied to the roller is transferred and applied to a support conveyed between this roller and another roller. Japanese Patent Application Laid-open No. 08-072227 (1996) similarly discloses a mechanism in an ink jet printing apparatus which applies a treatment liquid before printing which liquid insolubilizes dyes. In Embodiment 1 of this document, the treatment liquid in a replenishing tank is pumped by being attached to the rotating roller. At the same time, the treatment liquid pumped is applied to print paper.
With the configurations described in the above patent documents, an application liquid is applied or supplied to the surface of the rod bar or roller. However, the part of the rod bar or roller to which the application liquid is applied or supplied is open to or in communication with the air. Thus, disadvantageously, the application liquid may be evaporated or for example, the application liquid may leak when the posture of the apparatus is changed.
In particular, with an ink jet printing apparatus such as a printer, in view of, for example, the leakage of the liquid caused by a change in the posture of the apparatus, it is difficult to apply the applying mechanism described in the above documents to the apparatus if its size has been reduced.
In contrast, Japanese Patent Application Laid-open No. 08-058069 (1996) discloses a configuration that seals a part that applies or supplies inks, that is, application liquids, to a roller. The applying mechanism described in this document operates in a gravure printing apparatus to apply inks to a roller (applying roller) whose surface is formed with a pattern of a printing plate. This mechanism uses an ink chamber having two doctor blades arranged at two vertical positions along a peripheral surface of the roller and extending in a longitudinal direction of the roller and elastic members provided at the opposite sides of the two doctor blades. The chamber is contacted with the peripheral surface of the roller to form a liquid chamber between the ink chamber and the roller. Then, the roller is rotated to apply or supply the application liquid from the liquid chamber to the roller.
However, if the application liquid is left in the liquid chamber for a long time, then even with the appropriate sealing of the application liquid chamber, the evaporation of the application liquid from the liquid chamber may vary the concentration of the application liquid. This may result in unsatisfactory application.
Further, when the applying operation is not performed, if the applying roller remains in contact with or immersed in the applying liquid in the liquid chamber for a long time, then the applying liquid may degrade the applying roller.
Moreover, in spite of the appropriate sealing of the liquid chamber, the applying liquid may leak from the liquid chamber as a result of a change in the posture of the liquid applying apparatus such as a tilt. That is, if the liquid applying mechanism has a long structure, then in a normal applying posture, a longitudinal direction of the liquid applying mechanism corresponds to a horizontal direction. If the longitudinal direction of the liquid applying mechanism is changed so as to correspond to a vertical direction, a large difference occurs in water head between the upper side and lower side in the vertical direction, corresponding to the longitudinal direction. Pressure resulting from the difference in water head may cause the leakage of the liquid on the lower side in the vertical direction. Even if the longitudinal direction of the liquid applying mechanism is changed so as to correspond to a direction other than the vertical one, the leakage of the liquid may occur if a difference occurs in the water head between the upper side and lower side after the tilt. Therefore, the posture of the liquid applying apparatus during transportation or storage is limited. The liquid may leak from the liquid chamber unless the posture is carefully maintained.